Electrical issue exorcism

[Matt16]

I think have a short somewhere on my house circuit, specifically my dash panel wiper and nav light circuits. Anyone have any insight to resolving this. How should I use an ohm meter to find what I presume is a cross connection of two frayed wires? I have access to the rear of the dash panel. There are no obvious live wires dangling from the back of the dash panel.

Action

Outcome

turn on most dash switches	normal results, switches supply power as usual no gremlin
turn on navigation lights	nav lights come on all gauges (i.e. Mercruiser temp, oil, fuel, rpm, battery, temp) all go to 110% all other circuits on on the panel go dead cannot shut off the main engine
turn on wipers	nav lights come on (yes, nav lights come on, not wipers!) all gauges (i.e. Mercruiser temp, oil, fuel, rpm, battery, temp etc.) all go to 110% all other circuits on on the panel go dead cannot shut off the main engine

Thoughts/questions:
-Most(?) gauges read 100% when the encounter no resistance, right? So if all gauges are all pegged at 110%
-the issue was intermittent initially, but became more frequent, often happens in rough water (jarring)
-my main engine always starts and runs fine during the dash malfunction

 

[YachtMech]

I think have a short somewhere on my house circuit, specifically my dash panel wiper and nav light circuits. Anyone have any insight to resolving this. How should I use an ohm meter to find what I presume is a cross connection of two frayed wires? I have access to the rear of the dash panel. There are no obvious live wires dangling from the back of the dash panel.

Action

Outcome

turn on most dash switches	normal results, switches supply power as usual no gremlin
turn on navigation lights	nav lights come on all gauges (i.e. Mercruiser temp, oil, fuel, rpm, battery, temp) all go to 110% all other circuits on on the panel go dead cannot shut off the main engine
turn on wipers	nav lights come on (yes, nav lights come on, not wipers!) all gauges (i.e. Mercruiser temp, oil, fuel, rpm, battery, temp etc.) all go to 110% all other circuits on on the panel go dead cannot shut off the main engine

Thoughts/questions:
-Most(?) gauges read 100% when the encounter no resistance, right? So if all gauges are all pegged at 110%
-the issue was intermittent initially, but became more frequent, often happens in rough water (jarring)
-my main engine always starts and runs fine during the dash malfunction

sounds like a lose connection or chaffed wire, Check the connections of the switches at the power switched side of the nav and wipers, a lot of the time they are so close that if something moves they can touch and power up things that arent supposed to be or short cuircuit. the engine not shutting off means you are continuing to power the ignition cuircuit unintentionally


gauges are voltage sensitive through a range of voltages due to resistance, feed them a full 12.7+ volts and they will max out.

 

[Matt16]

sounds like a lose connection or chaffed wire, Check the connections of the switches at the power switched side of the nav and wipers, a lot of the time they are so close that if something moves they can touch and power up things that arent supposed to be or short cuircuit. the engine not shutting off means you are continuing to power the ignition cuircuit unintentionally


gauges are voltage sensitive through a range of voltages due to resistance, feed them a full 12.7+ volts and they will max out.

Thanks, this is helpful.

 

[YachtMech]

Thanks, this is helpful.

Or one of your buddies Has been messing with you, And intentionally cross connected or jumped power wires

 

[Matt16]

 

[Matt16]

Or one of your buddies Has been messing with you, And intentionally cross connected or jumped power wires

Wasn't it great when friends could actually join us on boats? lol

 

[noluck]

do the gauges work proper with the ignition switch, if you are in the lower mainland i could have a look at it

 

[ship happens]

I think have a short somewhere on my house circuit, specifically my dash panel wiper and nav light circuits. Anyone have any insight to resolving this. How should I use an ohm meter to find what I presume is a cross connection of two frayed wires? I have access to the rear of the dash panel. There are no obvious live wires dangling from the back of the dash panel.

Action

Outcome

turn on most dash switches	normal results, switches supply power as usual no gremlin
turn on navigation lights	nav lights come on all gauges (i.e. Mercruiser temp, oil, fuel, rpm, battery, temp) all go to 110% all other circuits on on the panel go dead cannot shut off the main engine
turn on wipers	nav lights come on (yes, nav lights come on, not wipers!) all gauges (i.e. Mercruiser temp, oil, fuel, rpm, battery, temp etc.) all go to 110% all other circuits on on the panel go dead cannot shut off the main engine

Thoughts/questions:
-Most(?) gauges read 100% when the encounter no resistance, right? So if all gauges are all pegged at 110%
-the issue was intermittent initially, but became more frequent, often happens in rough water (jarring)
-my main engine always starts and runs fine during the dash malfunction

Someone has the engines electrical harness ( ignition wire ) tied in with a constant power feed and some switches wired backwards.

 

[ericl]

Have there been any recent changes to the electrical system (last time something new was installed?)

Did everything ever work perfectly?

Each switch will have power from a fuse/breaker coming in, and power from the switch to the powered device going out. IMO this problem is isolated to the "powered device output from the switch". As mentioned above, the "tab" type connectors can easily come loose & make contact with another circuit. You may have more than one faulty connection.

You must first determine what wire is always hot & what wire is only hot when the switch is on for the wipers & lights. Measured in ohms, there should be a very low reading of less than 1 ohm between the 2 "always hot wires" and a very high reading/off the scale reading between the 2 "hot when switched" wires. Also check measured on the 20 volt scale that when all switches are off, none of the "hot when switched" wires have any voltage. It is useful to get an alligator clip to attach to one of your test points as trying to hold 2 meter probes in place while measuring is difficult.

Most likely the problem(s) are within a couple of inches of the panel.

 

[Matt16]

do the gauges work proper with the ignition switch, if you are in the lower mainland i could have a look at it

If the nav lights are off and the wipers are off, the key switch appears to work normally. Thats a generous offer, I'd compensate you for your time of course. Let me take another stab at it this weekend, then I'll call in the cavalry.

 

[Matt16]

Someone has the engines electrical harness ( ignition wire ) tied in with a constant power feed and some switches wired backwards.

Can you explain this a bit more? I bought the boat 2 years ago, worked fine, this set of issues first happened 6 months ago on a rough day, and then went away, now it is back to stay.

 

[noluck]

is the boat aluminum?

 

[Matt16]

is the boat aluminum?

No, its fiberglass, but the dash panel to which the switches and breakers are mounted is aluminum. I doesn't appear that this panel was designed to serve as a common ground.

 

[noluck]

No, its fiberglass, but the dash panel to which the switches and breakers are mounted is aluminum. I doesn't appear that this panel was designed to serve as a common ground.

this is a fun little problem you have, should be a quick easy fix

 

[noluck]

first thing i would do is remove the ground wires from the panel and put in a ground bus

 

[ericl]

Someone has the engines electrical harness ( ignition wire ) tied in with a constant power feed and some switches wired backwards.

No, its fiberglass, but the dash panel to which the switches and breakers are mounted is aluminum. I doesn't appear that this panel was designed to serve as a common ground.

On a boat all 12V DC grounds need to be connected to the neg battery terminal & the neg battery terminal needs to be connected to the proper part of the engine that assures the ground has contact with the water.

I have no experience with wiring mercruiser but it sounds like many/all of your panel accessory switches get power from the ignition switch? (do the wipers/nav lights work when the engine is shut-off?). IMO certain items such a bulge pumps & nav lights need to work with the engine off.

 

[ship happens]

Hire a pro, this conversation could get confusing

 

[noluck]

Hire a pro, this conversation could get confusing

that is why i offered to give a hand, easier than a bunch of typing

 

[ship happens]

Rodger that.

To the poster, the engine ignition circuit off the key switch. Should be purple or red. Should only power up the engine ignition circuit and the guages. That's it

 

[noluck]

did you find the problem?